Inverter Question

spanel
spanel Solar Expert Posts: 36 ✭✭
Im planning a smallish solar setup with a genertor backup... I will have a Transfer relay hooked up to the main breaker in the cabin.


So I know the genny get tied into one side of the relay and an inverter in the other...

My question is this..

Im looking at a 600 Watt Samlex Pure sine wave or maybe the 1000 watt. Both have 2 plugs for the 120. Do I just put a heavy duty cord in one outlet and splice the other end into the relay transfer switch?

Thanks!

p.s. All I would use the Inverter for is maybe 2 ceiling fans, 1/2 dozen CFL's.. I know the 1000 is overkill.. but maybe I want to use a microwave every now and then? Or just the 600 and get a small microwave or turn the genny on if i want to use that?

Thanks again!

Chris

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Inverter Question

    There's a couple of different ways you could go about this.

    First off, never mind the 1000 Watt unit for running a microwave: chances are good it won't do it. I have a "700 Watt" microwave, but that is a cooking power rating; it actually draws over 1000 watts. Your best bet is to fire the gen when needed for this.

    As to wiring it all in, if you don't want extension cords looped all over the place then yes you can feed a "main distribution panel" off a short, heavy cord plugged into the inverter. Remember that the inverter is going to "fault" before any breaker trips: 600 Watts is only 5 Amps @ 120 VAC and breakers tend to be 15 Amps.

    You will need some method of recharging the batteries from the generator. The Samlex units do not have built-in chargers, so you'll need a stand-alone battery charger. You can use a cheap, automotive type to do the bulk charging and then allow the solar panels to finish charging to proper levels through the controller.

    Another thing you might consider is wiring heavy loads to a distribution box, including a charger to feed the batteries. Then just connect the light loads to the inverter via a junction box. This way there is no transfer switch and the inverter's output is fully isolated from the gen's at all times.

    If I were you I'd think long term too; what will you want the system to do in the future It is possible to plan ahead for expansion at least a little bit if you take that into consideration.

    Most important is to get as accurate as possible numbers for expected use in terms of Watt hours per day. The whole design will hinge on that figure.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Inverter Question

    NO ! Don't splice a suicide cord to the inverter/transfer switch. yet.

    Please draw a line/block diagram of this, sometimes, just when you think you have it nailed, the smoke comes out of all the parts.

    Can your inverter have one leg grounded ? Can your generator ? Don't cross the grounded legs in the transfer switch ! You say Off-grid cabin, does that mean it was never connected to the grid or a power panel ? I'm thinking of old, hidden ground rods wired somewhere, or a water pipe ground.....

    Get a charger too, when you run the genset, use it's extra capacity to boost your batteries.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Inverter Question

    As Mike said, "clean" wiring is essential to any install. That's why I mentioned totally isolating one AC system from the other. watching out for extra, accidental grounds and neutral-ground bonds can be a problem. Samlex is a pure sine inverter and should have no trouble with 'standard' house wiring practices.

    If you get a handle on loads you might also consider a Morningstar 300 Watt inverter: http://www.solar-electric.com/mosu300wasiw.html They are well liked by many of the posters here, if that size would fit your needs.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Inverter Question

    Even a pair od sure sine 300s, with each wired to one side of the buss of a split phase panel, each powering given set of loads. I second the notion of not powering the microwave. A big current draw regardless of the inverter size. Starting current is likey to be much greater than the battery and inverter can handle.

    Tony
  • spanel
    spanel Solar Expert Posts: 36 ✭✭
    Re: Inverter Question

    This will be all from scratch.. the building is not even built yet.

    Thanks

    Chris
  • Paul54
    Paul54 Registered Users Posts: 18
    Re: Inverter Question

    I just checked the Samlex web site, and those particular models do not tolerate their "neutral" conductor to be grounded. If you are trying to transfer to existing branch circuits be sure your transfer switch can switch both hot and neutral. Also use a meter to be sure all the branch circuits are isolated completely from each other, with no hot neutral swaps or grounded neutrals downstream of the breaker panel.

    If you are putting in the wiring, just be sure to only bond neutrals and ground at your main panel, but do your transfer switch such that you remove the neutrals form the ground bond when using the Samlex. Do keep the Samlex's equipment ground connection tied to your main system ground at all times.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Inverter Question

    That is another advantage of the Suresine, it permits a grounded neutral.

    Tony
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Inverter Question
    icarus wrote: »
    That is another advantage of the Suresine, it permits a grounded neutral.

    Tony

    And, for short term (10 min) it's rated for 600W. That's sort of burried in the paperwork.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • spanel
    spanel Solar Expert Posts: 36 ✭✭
    Re: Inverter Question

    So basically what you guys are telling me, Im better off with the Morningstar because 300watts/600 surge is good enough to run a few CFLs and 1/2 ceiling fans... and its also easier to wire because I dont have to worry as much about grounding issues?

    Thanks!


    Chris
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Inverter Question

    That would be my suggestion.

    Unless you are routinely going to run near 300 watts of load, it is certainly would be my choice.

    T
  • spanel
    spanel Solar Expert Posts: 36 ✭✭
    Re: Inverter Question

    After much thought.... a tv/sat might be added to the mix down the road. If I needt to go a bit more than 300 but less than 500watts.. what would you guys suggest as far as inverters?

    thanks!

    p.s. Was thinking.. worst case senario..

    3 ceiling fans with 3 lights
    26" led tv.. looked like approx 50 startup 25 avg watts
    sat reciever 25 watts

    50watts approx for the fans, 13 watts cfls..

    117watts for the cfls, 150 for the fans.
    75 watts for tv/sat

    so we are at 342 watts.

    Thanks again!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Inverter Question

    What are you looking at for battery bank voltage and hours of usage per day...

    You are still looking at a small system and 12 volts is still very practical, but as your power usage goes up, your solar array and battery bank will get larger.

    You can save some significant money on higher voltage battery banks because many solar charge controllers are rated at 12/24/48 volt output. 24 volt will handle 2x the power as 12 volt, and 48 volt 4x the power as 12 volt...

    Larger MPPT type charge controllers are not cheap, and upping the battery bank voltage can allow you to stay with one charge controller instead of 2 or more. Smallest good quality MPPT is 15 amps (Morning Star 12/24 volt output). And there are 30 amp, 45 amp, 60 amp, 80+ amp MPPT's too...
    • 15 amp * 14.5 volts * 1/0.77 derating = 282 watts optimum maximum solar array
    • 15 amp * 14.5 volts * 1/0.77 derating = 565 watts optimum maximum solar array
    • etc.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • spanel
    spanel Solar Expert Posts: 36 ✭✭
    Re: Inverter Question

    for the most part.. we will have a genny running during the day.. the load refered above...

    at most all things would run 2-3 hrs. Maybe 1 fan all night (8hrs).

    Looking at 4 -t105re trogans.
    135watt solar panel
    genny charging during the day when neccesary.


    Chris
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Inverter Question

    Chris,
    spanel wrote: »
    for the most part.. we will have a genny running during the day.. the load referred above...

    at most all things would run 2-3 hrs. Maybe 1 fan all night (8hrs).
    117watts for the cfls, 150 for the fans.
    75 watts for tv/sat

    (117w + 150w + 75w) * 3 hours = 1,026 Watt*Hours
    50 watt fan * 8 hours = 400 Watt*hours
    ==================================
    1,426 WH of 120 VAC power per night

    Assuming 2 days of no sun (1-3 days recommended) and 50% maximum discharge for battery bank:
    • 1,426 WH * 1/0.85 inverter eff * 2 days * 1/0.50 max discharge = 559 AH @ 12 volt battery bank
    Minimum solar array assuming at least 4 hours of full sun per day (usually around 9 months a year for many locations):
    • 1,426 WH * 1/0.52 derating * 1/4 hours of sun per day = 686 watts of solar panel minimum
    Optimal battery bank charging with solar panel (5-13% typical rule of thumb, ~10% rate of charge for flooded cell batteries as optimum):
    • 559 AH * 14.5 volts * 1/0.77 derating * 0.10 rate of charge = 1,053 AH "optimum" solar array for flooded cell battery bank
    Looking at 4 -t105re Trojans.
    135watt solar panel
    genny charging during the day when necessary.

    Your 4xT105RE batteries at 6 volts each (225AH) would be 450 AH @ 12 volts... A bit small, but within reason.

    Your solar panel is way too small for the daily loads--You would need to use the genset to get the battery bank recharged.

    Unless you are thinking about reducing the loads somewhat... Most people underestimate their loads and over estimate what a solar PV system can supply.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • spanel
    spanel Solar Expert Posts: 36 ✭✭
    Re: Inverter Question

    It wont be a daily residence.... fri/sat night only when used.

    Chris
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Inverter Question

    Personally, I would use a Honda eu1000i/eu2000i for the 3 hour evening loads and use the battery for fan/random lighting at night... And a smaller battery bank to better match the solar array, lesser needs.

    You don't want to discharge the battery to 50% and then let it take 5 days to recharge with a small solar array--More than likely, the batteries will die sooner (year or so?) because of sulphation during the time it takes to recharge from 50% to >75%... Of course, you can use a genset on Sunday morning to quickly recharge the larger batter bank above 75% state of charge, and let the solar array finish them off (when needed).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Inverter Question

    Consider using two sure sine 300s each wired to one side of a slit phase buss.

    Then wire your loads so that they are split between e two busses. The standby/idle current of the sure sine is small enough not to e a real problem, and they are quite efficient.

    Tony
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Inverter Question

    re: using the 300w inverter for a TV/Sat/ receiver,
    you could test the inverter at home (use a car battery for 12v test) to see if it will handle the load. If not get a second slightly larger inverter...

    hth.
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
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